1. Field of the Inventions
The suggested inventions relate to the intra-vision means and are designed for producing visually sensed images of the internal structure of an object, in particular, of a biological object, with X-rays. The preferential applications include defectoscopy and medical diagnostics.
2. Description of the Prior Art
Various methods and devices of the said intended use are known, where traditional principles of projection roentgenoscopy are embodied. In such methods and devices, the visible image of the object""s internal structure, for example, tissues of a biological object, is obtained as a shadow projection. Density of the acquired image in each of its points is determined by the total attenuation of X-rays that passed through the object on their way from the source to the detection means. The latter is either a fluorescent screen or an X-ray film, which should be chemically treated to get the image visualized (see Polytechnical Dictionary. Moscow, xe2x80x9cSoviet Encyclopediaxe2x80x9d, 1976 [1], p.425; Physics of image visualization in medicine. Edited by S. Webb. Moscow, xe2x80x9cMirxe2x80x9d, 1991 [2], p. 40-41).
In the above mentioned known methods and devices, the image of a real three-dimensional structure is acquired as the said two-dimensional shadow projection, which interpretation requires from the specialist who carries out object analysis, in particular, technical or medical diagnostics, respective experience and qualification and, in a number of cases, is problematic. The reasons for this are low contrast, poor signal to noise ratio, inevitable overlapping of the images of structural elements, impossibility of quantitative comparison between individual local fragments by density. Sharpness and contrast of the acquired image also decrease under the influence of quanta of the secondary Compton scattered radiation, hitting the detection means.
X-ray computer tomography methods and devices permitting to acquire a two-dimensional image of a thin layer of a three-dimensional object are known (V. V. Piklov, N. G. Preobrazhenskiy. Computational tomography and physical experiment. The progress of physical sciences, v. 141, 3rd ed., November 1983, p. 469-498 [3]; see also [2], p. 138-146). Such methods are using multiple irradiation of the object under study from different positions and registration of the radiation that passed through this object by a line of detectors. The obtained tissue density distribution of the object in the cross-section under study (target cross-section) is discrete and achieved through computer-assisted solution of combined equations, the order of which as well as the number of resolution elements correspond to the product of the number of positions, from which irradiation is done, by the number of detectors. Doing irradiation in different cross-sections, one can obtain a three-dimensional image of the object based on a set of two-dimensional by-layer images. Computer tomography means permit in principle to obtain an image of sufficiently high quality, and this image presents the picture of tissues density distribution (in contrast to a picture specific to integral absorption of a substance (for example, biological tissues), located in the path of radiation from the source to this or that element of the observed projection.) But this is achieved through a greater number of positions, from which irradiation is done. In this case, the dose of radiation absorbed by the substance is higher, which is undesirable (and in medical applications, is most frequently inadmissible). Presence of Compton scattered radiation is a nuisance factor in this group of known methods and devices too. Both groups of methods and devices used for medical applications are also characterized by the fact, that tissues and organs, which present no interest in the study but are located in the radiation path (both in front and behind the target area), also suffer from intensive radiation (to a lesser degree in the second group of methods and devices than in the first group of methods and devices because when different positions are selected, different tissues and organs surrounding those that are under study are irradiated).
Higher resolving power in the second group of means, requiring a greater number of irradiations from different positions, is limited, first of all, due to inadmissible growth of the dosage. Technical means for acquiring primary data and further image reconstruction is quite complex due to necessity of using fast computers with special software and high-precision requirements to the mechanical structural elements, which must guarantee correct localization of one and the same resolution elements in the target area during their irradiation from different positions. The latter is caused by the fact that the image reconstruction calculations must use the actual data obtained from different irradiation cycles but referring to one and the same resolution elements.
The second above mentioned group of methods and devices, where discrete data on the density of each of the resolution elements is obtained, is the closest one to what is suggested.
The technical result, which the suggested inventions are aimed at, consists in higher accuracy of determining relative indices of the object""s substance density in the acquired image together with avoided use of complex and expensive technical means. When the suggested inventions are used for diagnostic purposes in medicine and other investigations related to the action on biological objects, the achieved result consists also in reduced dosage of radiation of tissues surrounding the tissues under study.
To obtain the said types of technical results, in the suggested X-ray method of producing the image of the internal structure of an object, the X-rays are concentrated in a zone, which is located inside the area under study (which area is hereinafter referred to as the target area) of the object. Secondary radiation (scattered Compton coherent and non-coherent, fluorescent radiation), excited in this zone, is transported to one or more detectors. Scanning of the target area of the object is done by way of moving the zone of concentration. The results of measurement at each current position of the zone of concentration (X-rays concentration zone) are attributed to one of the points inside this zone. Movement of the zone of concentration during scanning is followed by simultaneous determination and fixation of coordinates of this zone. Judgment on the density of the object""s substance in this point is made based on the population of intensity values of the secondary radiation, which are obtained with the help of one or more detectors and which are determined simultaneously with the coordinates of the said current point. The obtained values, recognized as the density indices of the object""s substance, together with respective values of coordinates, are used for building up a picture of the substance density distribution in the object""s target area. Movement of the X-ray concentration zone for scanning the object""s target area is done by way of relative movement of the object under study and the X-ray sources, which relative position between themselves remains stable, together with the X-ray concentration means, means for secondary radiation transportation to the detectors, and the detectors themselves.
A common feature for the known from ([2], pp. 138-146, [3], pp. 471-472) and suggested methods is the action on the object under study with X-rays during relative movement of the object under study and the X-ray optical system including X-ray sources together with their control units and detectors.
One of the differences of the suggested method consists in the presence of the operation of concentrating X-rays in the zone covering the current point, in which it is required to determine a density value (a current point, to which the measurement results are attributed). Scanning, which presence is a common feature of the known and suggested methods, is done in a totally different way in case of the latterxe2x80x94by shifting the current position of the X-rays concentration zone into the vicinity of the next point, for which it is desirable to determine the density of the substance of the object under study. The difference consists also in the operation of transportation of the secondary radiation (scattered Compton coherent and non-coherent radiation, fluorescent radiation), excited in this zone, from the concentration zone to the detector (detectors).
In this instance, it is not the radiation of the source itself, which passed through the object under study, that renders action on the detector (detectors), but the said secondary radiation. Intensity of the latter, as is well known (see J. Jackson. Classical Electrodynamics. M., xe2x80x9cMirxe2x80x9d, 1965, pp. 537-538 [4]), when all other conditions are the same, is proportional to the density of the substance, in which this radiation is excited, regardless of the nature of this substance. Thanks to this, secondary scattered radiation, which is a nuisance factor in the known method, becomes an informative factor. Usage of current values of the secondary radiation intensity as an index of the substance density is another difference of the suggested method.
Differences of the suggested method from the known one are also characterized below, in the description of possible particular cases of its embodiment, providing for using various combinations of X-rays concentration means and transportation means for the secondary scattered radiation.
In one of such particular cases, X-rays concentration in the zone covering the current point, to which the measurement results are attributed, is done using one or more collimators. In this case, a respective number of space-apart X-ray sources are used. Transportation of the excited secondary radiation to one or more detectors is also done using one or more collimators, where all collimators are oriented so that the axes of their central channels would cross in the current point, to which the measurement results are attributed.
In another particular case, X-rays concentration in the zone is done using one or more X-ray hemilenses transforming divergent radiation of a respective number of X-ray sources into quasi-parallel radiation. Transportation of the excited secondary radiation to one or more detectors is done, in this case, using one or more X-ray hemilenses or lenses, focusing this radiation on the detectors. It is also possible to perform transportation of the secondary radiation to one or more detectors using one or more hemilenses forming quasi-parallel radiation. In this case, all X-ray lenses and hemilenses are oriented so that their optical axes would cross in the current point, to which the measurement results are attributed.
In still another particular case X-rays concentration in the zone is done using one or more X-ray hemilenses transforming the divergent radiation of a respective number of space-apart sources into quasi-parallel radiation, while transportation of the excited secondary radiation to one or more detectors is done using one or more collimators. In this case, the X-ray hemilenses and collimators are oriented so that the optical axes of all X-ray hemilenses and central channels of all collimators would cross in the current point, to which the measurement results are attributed.
X-rays concentration can be also done using one or more space-apart X-ray sources and a respective number of X-ray lenses focusing the divergent X-rays from each of the sources directly in the current point, to which the measurement results are attributed; while transportation of the excited secondary radiation to one or more detectors is done using X-ray lenses focusing this radiation on the detectors and having a second focus in the said point.
Another particular case differs from the previous one in that the transportation of excited secondary radiation to one or more detectors is done using collimators oriented so, that the optical axes of their central channels would cross in the output focus of the lens focusing divergent radiation from the source (in the common focus of more than one such lenses if more than one sources are used).
The suggested device for producing the image of the internal structure of an object with X-rays comprises a means for positioning the object under study, an X-ray optical system, a means for relative movement of the means for positioning the object under study and the X-ray optical system, a means for data processing and imaging. The device also comprises sensors for determining the coordinates of the current point, to which the measurement results are attributed and which is located inside the target area. These sensors are linked to the means for positioning of the object under study and the X-ray optical system and connected through their outlets to the means for data processing and imaging. The X-ray optical system comprises one or more X-ray sources, means for concentration of the radiation from the said one or more X-ray sources in the zone covering the current point, to which the measurement results are attributed. In addition the X-ray optical system comprises one or more means for transportation of the excited secondary radiation and placed at their exits detectors of this radiation. The outlets of the said detectors are connected to the means for data processing and imaging.
A common feature of the known and suggested devices is the presence of the means for positioning the object under study, an X-ray optical system, a means for relative movement of the means for positioning the object under study and the X-ray optical system, coordinate sensors, and the means for data processing and imaging.
In contrast to the known device, the X-ray optical system in the suggested device comprises means for concentration of the radiation from one or more sources in the zone covering the current point, to which the measurement results are attributed. In addition, the X-ray optical system comprises one or more means for transportation of the excited secondary radiation to the detectors of this radiation. Thanks to this, it is this radiation that is input to the detectors but not the radiation from the source (sources) after it has passed through the object under study. The coordinate sensors in the suggested device fulfill another function compared with the known devicexe2x80x94they are used for determining coordinates of the current point, to which the measurement results are attributed. The function of the means for data processing and imaging is also differentxe2x80x94this means acts based on the input carrying direct data on the substance density and coordinates of the current point, to which these data are attributed. The design of the suggested device and its principle of operation create prerequisites for a situation, when there is no dependence on the accuracy or resolving power, since the performance characteristics for this device are practically fully determined by the parameters of the X-rays concentration means used.
Other differences featured by the suggested device, in various possible particular cases of its embodiment, are characterized below.
In one of such particular cases, the X-ray optical system of the suggested device includes more than one X-ray sources. In this instance, each of the means for X-rays concentration and each of the means for transportation of the excited secondary radiation to detectors are made as a collimator with its channels oriented towards the zone of concentration of the radiation from the X-ray sources. The optical axes of the central channels of all collimators cross in the current point, to which the measurement results are attributed.
In this particular case, the X-ray sources incorporated in the X-ray optical system can be quasi-point. The collimators have channels that are all focused on these sources and are fanning (widening) towards the means for positioning the object under study. Between the exit from each X-ray source and entrance to a respective collimator, there is a screen with an opening.
In the same particular case, the X-ray sources incorporated in the X-ray optical system can be extended X-ray sources. In this instance, the collimators have channels that are all coming together (narrowing down) towards the means for positioning the object under study.
In another particular case of embodiment of the suggested device, the X-ray sources incorporated in the X-ray optical system are quasi-point sources; each of the means for X-rays concentration is made as an X-ray hemilens transforming the divergent radiation of a respective source into quasi-parallel radiation; while each of the means for transportation of the excited secondary scattered Compton radiation to the detector is made as an X-ray hemilens focusing this radiation on the detector. In this instance, the optical axes of all X-ray hemilenses cross in the current point, to which the measurement results are attributed.
In the next particular case of embodiment of the suggested device, same as in the previous one, the X-ray sources incorporated in the X-ray optical system are quasi-point sources, and each of the means for X-rays concentration is made as an X-ray hemilens transforming the divergent radiation of a respective source into quasi-parallel radiation. But in contrast to the previous case, each of the means for transportation of the excited secondary radiation to the detector is made as an X-ray hemilens with its focus in the current point, to which the measurement results are attributed, which hemilens transforms the said radiation into quasi-parallel radiation and directs it to the detector. In this instance, the optical axes of all X-ray hemilenses cross in the current point, to which the measurement results are attributed.
In still another particular case, the X-ray sources incorporated in the X-ray optical system are also quasi-point sources; each of the means for X-rays concentration is made as an X-ray hemilens transforming the divergent radiation of a respective source into quasi-parallel radiation. But in contrast to the previous case, each of the means for transportation of the excited secondary radiation to the detector is made as an X-ray lens focusing this radiation on the detector and having a second focus in the X-rays concentration zone. The optical axes of all X-ray hemilenses and lenses cross in the current point, to which the measurement results are attributed.
In the next particular case, same as in the previous two, the X-ray sources incorporated in the X-ray optical system are quasi-point, and each of the means for X-rays concentration is made as an X-ray hemilens transforming the divergent radiation of a respective source into quasi-parallel radiation. In this instance, each of the means for transportation of the excited secondary radiation to the detector is made as a collimator with channels that are all fanning (widening) towards a respective detector. The optical axes of all X-ray hemilenses and central channels of collimators cross in the current point, to which the measurement results are attributed.
The X-ray optical system of the suggested device can be made as follows too. The X-ray sources incorporated therein are quasi-point sources; each of the means for X-rays concentration is made as an X-ray hemilens transforming the divergent radiation of a respective X-ray source into quasi-parallel radiation; while each of the means for transportation of the excited secondary Compton radiation to the detector is made as a collimator with channels that are all coming together (narrowing down) towards a respective detector. The optical axes of all X-ray hemilenses and central channels of collimators cross in the current point, to which the measurement results are attributed.
Another embodiment of the suggested device is also possible, where the X-ray sources incorporated in the X-ray optical system are quasi-point sources; each of the means for X-rays concentration is made as an X-ray lens focusing the divergent radiation of the X-ray source. In this instance, each of the means for transportation of excited secondary radiation to the detector is made as an X-ray lens focusing this radiation on a respective detector. The optical axes of all X-ray lenses cross in the current point, to which the measurement results are attributed.
Next particular case of embodiment of the suggested device is characterized by the fact that the X-ray sources incorporated in the X-ray optical system are quasi-point sources; each of the means for X-rays concentration is made as an X-ray lens focusing the divergent radiation of the source; while each of the means for transportation of the excited secondary radiation to the source is made as a collimator with its channels narrowing down (coming together) towards a respective detector. In this instance, the optical axes of all X-ray lenses and central channels of collimators cross in the current point, to which the measurement results are attributed.
One more particular case of the device embodiment is characterized by the fact that the X-ray sources incorporated in the X-ray optical system are quasi-point sources; each of the means for X-rays concentration is made as an X-ray lens focusing the divergent radiation of the X-ray source; while each of the means for transportation of the excited secondary Compton radiation to the detector is made as a collimator with channels widening (fanning) towards a respective detector. In this instance, the optical axes of all X-ray lenses and central channels of collimators cross in the current point, to which the measurement results are attributed.